Generally, due to the characteristics of light weight, slim thickness, low electric power consumption, the liquid crystal display device (or, LCD) is being widely applied. The LCD displays a picture data (or an image) by using the physical property of crystal that changes array in response to voltage or temperature.
As LCD is not a self-luminescent element, the LCD requires a backlight unit for irradiating light to the liquid crystal display panel. There are two kinds of the backlight units for LCD, one is the direct type backlight unit and the other is the edge type backlight system. The most common LCD shows the picture data by modulating the luminescence of the light incident from the backlight unit by controlling the electric field applied to the liquid crystal layer.
For the edge type backlight unit, light source such as a fluorescent light source is equipped at the circumferences of the transparent light guide panel. The light radiated from the fluorescent light source to the side surface of the light guide panel is refracted and/or reflected to the front side on which an LCD panel is disposed. On the other hands, for the direct type backlight unit, a plurality of fluorescent light sources are disposed under the back side of the LCD panel so that the light is directly radiated from the light source to the overall surface of the LCD panel.
However, the abovementioned backlight units suffer from disadvantages of light being irregularly radiated to the LCD panel. As a result, the physical properties of LCD may be degraded. Thus there is required an effort to improve brightness uniformity of the LCD.